Odor detection in mice is mediated by approximately 1000 different odorant receptors (ORs), which are expressed by olfactory sensory neurons (OSNs) in the olfactory epithelium (OE) of the nose. Each OSN expresses only one OR allele and OSNs with the same OR are scattered in the OE. However, their axons converge in a representative pair of glomeruli in the olfactory bulb (OB), producing a stereotyped map in which each glomerulus is dedicated to one OR. In addition to its role in recognizing odorants, there is growing evidence that the OR may also play a role in guiding the developing OSN axon to the correct target glomerulus in the OB. The evidence stems from OR gene swapping and deletion experiments and observations of OR protein in OSN axons. Is the axonal OR protein required for glomerular targeting? If so, what is the mechanism? We propose to investigate these questions. Using proteomic methods, we will identify proteins that are associated with ORs on axons versus cilia to explore the possible roles of axonal ORs. By doing so, we hope to better understand how axonal ORs may influence glomerular targeting.